The role of intraovarian sex hormones in mediating gonadotrophic stimulation of follicular maturation, including atresia and oogenesis is being studied in vivo and in vitro. These studies indicate that estrogens stimulate while androgens inhibit granulosa cell proliferation and enhance atresia during preantral stages of follicular maturation. Since ovarian biosynthesis of androgen requires LH stimulation, but biosynthesis of estradiol requires FSH stimulation, the role of gonadotropins in stimulating both growth and atresia is mediated by sex steroid hormone synthesis.